Abstract:

In Manitoba, insecticidal applications are made to control the overwintering stage of the the Dutch elm disease vector, Hylurgopinus rufipes (Eichhoff). Unfortunately, little has been published about the exact location of overwintering H. rufipes in Manitoba. Thus the objective of this thesis is to examine the overwintering biology of H. rufipes in Manitoba with particular reference to the species, size, and location of the tree in which overwintering occurs, and the particular location of overwintering beetles on the tree. To accomplish the first part of the objective, three sites near Winnipeg where Siberian and American elms coexisted were selected. Entrance holes were counted at weekly intervals in the bottom 35 cm of the trunks of the trees during the fall of 1992. Hylurgopinus refipes was able to overwinter in Siberian elms, but overwintering in Siberian elms occured only where siberian elms were relatively close to American elm and where there was a high population density of H. rufipes... Ninety-five percent of the overwintering H. rufipes were found on trees greater than 15 cm DBH. The density of overwintering beetles did not increase with tree size above this size. In spring, no living beetles were found on trees less than 8 cm DBH. The accumulation of entrance holes was significantly greater in natural riverbank American elms than in adjacent planted trees. Ninety-six percent of the overwintering H. rufipes were found in the ground to 25 cm height range, whereas only about 50% of the holes and tunnels were found in this height range. It is likely that holes and tunnels above this range were made during feeding activity. Aspect and the area of root flare had no effect on the density of H. rufipes in a sample. Insecticidal applications may be restricted to the bottom 55 cm of American elms greater than 15 cm DBH. When H. rufipes are abundant, Siberian elms near American elms should also be treated.